Caderno Lab. Xeolóxico de Laxe Coruña. 1995. Vol. 20, pp. 253-279 A typological classification of Spanish precious metals deposits Clasificación tipológica de los yacimientos españoles de metales nobles CASTROVIE]O, R. Last decade's intensive exploration for precious metals in Spain led to a new understanding ofvarious types ofdeposits and prospects. A summary review of recent progress is presented, allowing the systematic (typological) classification of the Spanish precious metals deposits shown in Table 1: 19 types are defined in the framework of the Iberian Geology, their exploration significance being also considered. Hypogene deposits in the Hercynian Hesperian Massif, and epithermal gold deposits in the Neogene calc-alcaline Volcanic Province ofSE Spain have been very much explored and are therefore emphasized, although their mining production is by far not to compare with the precious metals output the SWIPB (SW Iberian Pyrite Belt). In the Hesperian Massif, different metalloterts have been demonstrated to be related to attractive concentrations ofgold, bound to Hercynian shear-zones, in Galicia, in Extremadura, etc.; other concentrations (e. g., in Galicia and Asturias) are related to granite or porphyry intrusions (Salave) and skarn formations (Carlés). PGE or Platinum elements (± chromite) have been found in ophiolitic thrust complexes occurring in N Galicia, e. g. the Herbeira Massifofthe Cabo Ortegal Complex, as had been in the 1940's in N orthern Portugal (Bragan\a and Morais complexes). Exploration for silver has demonstrated a small orebody in Fuenteheridos (Aracena, SW Spain), not minable under severe environmental constraints, but none ofthe classic Spanish silver producing districs (vein-Type deposits, e. g. Guadalcanal or Hiendelaencina) has recovered activity. Most of the EU (European Union) gold and silver production is won from only two types of deposits in the Spanish Hesperian Massif: the masive sulphides of the SWIPB, in which precious metals are won as by-products, and the related gossan deposits. 254 Castroviejo CAD. LAB. XEOL. LAXE 20 (1995) In the Alpine domains, the SE Spanish volcanic region (Almería-Murcia), has for centuries been worked for Pb-Ag-Zn-(Cu) and for Sn (Fe) and is presently well know for its epithermal gold and silver mineralizations (e. g. Rodalquilar and Transacción mines, Almería), but its full potential has yet to be realized. Recent work has shown epithermal precious metal-bearing bodies to occur in an area spreading over one hundred Km. northwards from those mines, and demonstrated the feasibility oftheir detection by remote sensing. Sediment-hosted epithermal deposits have not yet been found in the region, but are not to be excluded. An attractive, possibly economic, base metal and silverprospect is under investigation near Mazarrón (Murcia). In another context, the ultramafic massifs of the Serranía de Ronda (Málaga) are know as PGE metallotects, in which a new type ofPGE mineralization has been recently defined. On the other hand, exploration for gold in the Hercynian Basement of Alpine domains has also shown interesting prospects to occur, as in the pyreneean Vall de Ribes district. Finally, the formerly very important detrital (paleo-placer and placer) gold concentrations of Neogene to Quaternary age, occurring mainly in NW Spain although explored by various companies, did not lead to any mining activity yet. The overall picture of these years of research is an increased knowledge of the Spanish precious metals ore geology, the full reconnaissance and higher mining production of the gossan bodies of the SWIPB and the development of several prospects (Carlés-Salas, Salave, Fuenteheridos, Mazarrón, etc.) and of a gold mine (Transacción, Almería, of ephemeral activity). On the other hand, sorne questions have arisen which define interesting goals for future research, as the precise models of the different types of shear-zone orebodies, the evolution at depth of the Au-Ag orebodies in the known epithermal districts (e. g. Cabo de Gata, Almería), and the regional extent and exploration of thes.e orebodies (partly, under metamorphic and sedimentary Hercynian formations) in the SE Spain Neogene volcanic province, as well as the possible existence of disseminated, sediment-hosted Carlin-Type ore bodies. Key words: Gold, Silver, Platinum Group Metals, Typology, Metallogeny, Hercynian, Alpine, Spain, Exploration Geology. CASTROVIEJO, R. (Dpto. Ingeniería Geológica. E. T. S. Ing. de Minas, Universidad Politécnica de Madrid. el Ríos Rosas, 21, 28003-Madrid) 255 Clasificación metales nobles CAD. LAB. XEOL. LAXE 20 (1995) Cuadro 1 CLASIFICACION TIPOLOGICA ESPAAOLES DE METALES NOBLES YACIMIENTOS DE Tipo letal (tI Eje.pIo Caracterización CONCENTRACIONES MGP EN COMPLEJOS MAFICOS / ULTRAMAFICOS 1 MGP En el Macizo Hespérico: t. Ofiolítico C. Ortegal 2 MGP En dominios Alpinos: asoe. Cr-Ni (PGE-Au) s. Ronda CONCENTRACIONES MGP EN SEDIMENTOS Y SUELOS 3 MGP Detríticas / residuales, de tipos 1/2 íd. 1 , 2 CONCENTRACIONES DE Ag o Pb-Zn-Ag(**) EN TERRENOS HERCINICOS 4 Ag Filones argentíferos en rocas leta.órficas Hercínicas Guadalcanal 5 Ag Henas Ag en formaciones volcano-sedilentarias y carbonatadas Aracena t Hue 1va 6 Ag Filones hidrotermales Pb-Zn-(Ag) Linares CONCENT1S • Pb,Zn/Ag EN PROV. VOLCANICA NEOGENA DEL SE ESPAÑOL 7 Ag Rn relación con intrusiones sOleras Neógenas en rocas pre-Terc. La Unión 8 Ag Concentr. epiterlales relace volcanitas Neógenas calco-alcalinas Cabo de Gata CONCENT1S • VOLCANO-SEDIMENTARIAS EN EL MACIZO HESPERICO (*t*J 9 Au Diseminaciones Au en sulfuros masivos Huelva CONCENrS • HIPOGENICAS Au EN TERRENOS METAMORFICOS HERCINICOS 10 Au Filonianas, en zona de cizalla Fervenza 11 Au Hidrotermales, relace con granitoides Salave 12 Au Mixtas (z.cizalla en granitoides) Corcoesto 13 Au En formaciones de skarn con sulfuros Carlés 14 Au Filones Sb(As)~Au y otros Extreladura t León CONCENrS • Au EN PROVINCIA VOLCANICA NEOGENA DEL SE EspARoL 15 Au Encajante volcánico, tipo ácido-sulfatado (high-sulfidation) Rodalquilar 16 Au Encajante volcánico, tipo adularia-sericita (lofl-sulfidation) Cabo de Gata 17 Au Encajante no volcánico LOlo de Bas CONCENT1S • Au EN SEDIMENTOS DETRITICOS NEOGENOS y RECIENTES 18 Au Paleoplaceres t en especial Neógenos t y placeres auríferos NO Peninsular DEPOSITOS DE METALES PRECIOSOS EN FORMACIONES DE GOSSAN 19 Au Concentr. superg. Au-Ag en gossan de sulfuros lasivos (tipo 9) (*) Au. Ag J IGP o platílJidoB (letales del grupo del platiDo). (**) In 10B tipoB 6 J 1 la plata Bólo Be ha beDeficiado COlO sub-producto. (***) In el tipo 9, oro J plata se benefician COlO sub-productoB. Huelva 256 Castroviejo INTRODUCTION This contribution aims at summarizing recent progress in the Spanish precious metals geology, after a decade of active exploration. Emphasis is laid on the interpretation and systematic classification of deposits, exploration achievements being discussed by CASTROVIE]O (1994) in another papero This work is based on the own experience of the author and on published data or personal communications. The irregularity or scarcity of published data -exploration companies not always wanting their information to be published- is a major limitation, since confidential data are not going to be discussed. Gold has been the most explored (and is still the most important) precious metal in Spain, a country that is the first gold producer of the European Union (EU): its annual metal output in the last years is around 7 t, which accounts for about 60 % of the total EU mining production, while the 270 t ofsilver produced in 1990 account for over 63 % of the total EU mining output of 426.5 t (ITGE, 1990; t.he most recent evolution ofthe SWIPB mining activity points to a declining production at present). Most of the Spanish gold and silver production is won from the oxidized outcrops of massive sulphide orebodies in the SW Iberian Pyrite Belt (Huelva and Sevilla provinces), and as byproducts from thesesulphides. Platinum Group Metals (PGE) have never reached the level of mining production in the Iberian Peninsula. CAD. LAB. XEOL. LAXE 20 (1995) PROPOSAL OF A TYPOLOGICAL CLASSIFICATION Previous schemes and discussion of classification criteria The present classification considers each precious metal by itself, being gold the central subject, not only because of its mining significance, but also because many of the criteria used for gold are also valid for silver -whose Spanish mining production is mostly associated with gold- and because the relatively scarce PGE prospects in Spain can be easily classified into just a few types. Earlier typologies, both ofthem for gold, are included in the compilations by ].Burkhalter(IGME, 1984)andbyCRESPO (1988). The one used by the first author, following that of BACHE (1980), has the evident limitations recognized by the author himselfl, which are mainly due to the scarcity of previous work on Spanish precious metals deposits, rendering systematic comparisons difficult. Nevertheless he has grouped and compared similar Spanish deposits -in the sequence shown in Table 1-, and his work has not lost its unquestionable value as the most qualified inventory providing general information on Spanish gold deposits and prospects. The more recent proposal by CRESPO (1988) establishes seven types (Table 2) but does not include much geological information known or published later, making a more updated classification advisable 2 . The present work does not aim at such a comprehensive compilation as that of ]. Burkhalter; instead, only those deposits or prospects have been included that are considered to be significant or typical because of their geologic/mining features. Insignificant or geologically unknown occur- elasificación metales nobles CAD. LAB. XEOL. LAXE 20 (995) 257 TABLE 1 MAIN TYPES/DISTRICTS OF SPANISH GOLD DEPOSITS AFTER J. BURHKHALTER (IGKE, 1984) 1.2.3.4.5. 6.7.8.9.1011- Primary deposits of the Asturian Are (ASTURIAS-LEON) CABO DE GATA-RODALQUILAR (ALMERIA) Precambrian Alcudian Domain (VALLE DE ALCUDIA) Pyrite Belt (HUELVA-SEVILLA) LA NAVA DE RICOMALILLO (TOLEDO) Y SAN PABLO-MOLINILLO (CIUDAD REAL) LA NAVA DE JADRAQUE (GUADALAJARA) Galician deposits (LA CORUÑA - ORENSE) Detrital formations (in NW SPAIN and in SIERRA NEVADA) Area of LAS HURDES (CACERES - BADAJOZ) Gold-antirnony Belt (CACERES - BADAJOZ) Eastern pyrenees (GERONA) TABLE 2 TYPOLOGY OF SPANISH GOLD DEPOSITS AFTER VI CRESPO (1988) 1. DISSEMINATION IN HIGH-GRADE METAMORPHIC ROCKS: Nava de Jadraque. 2. DISSEMINATION OR QUARTZ-VEINLETS IN LOW TO MEDIUM-GRADE METAMORPHIC ROCKS: Valle de Alcudia, etc. 3. ASSOCIATED TO COMPLEX SULPHIDES: Pyrite Belt. 4. HERCYNIAN DEPOSITS (several subtypes: disserninated in granites; in quartz veins, etc.). 5. ASSOCIATED TO TRIASSIC Cu RED-BED TYPE DETRITAL ROCKS: Santonera. 6. VOLCANISM WITH FREE GOLD AND TELLURIDES: Rodalquilar. 7. PLACERS: Las Médulas, etc. 258 Castroviejo CAD. LAB. XEüL. LAXE 20 (1995) TABLE 3 A TYPOLOGICAL CLASSIFICATION OF SPANISH PRECIOUS METALS DEPOSITS 'Jpe Iletal Characterizacion (t) Example PGE CONCENTRATIONS IN MAFIC / ULTRAMAFIC COMPLEXES 1 PGE In Hesperian Massif: Ophiolitic t. c. 2 PGE In Alpine domains: Cr-Ni ores, with PGE/Au S. Ronda Ortegal PGE CONCENTRATIONS IN SEDIMENTOS AND SOILS 3 PGE Detrital / residual, from types 1 & 2 íd. 1, 2 Ag/bmAg (=BASE METAL-Ag )(tt) DEPOSITS IN HERCYNIAN TERRAINS 4 Ag Vein-type Ag deposits in Hercynian letallorphic terrains Guadalcanal 5 Ag Ag ores in volcanic-sedillentary and carbonate forllations Aracena, Hue 1va Vein-type Pb-Zn-(Ag) deposits Linares 6 Ag Ag/bmAg DEPOSITS IN THE NEOGENE VOLCANIC PROV. OF SE. SPAIN 7 Ag Vo lcanic- re lated baAg lIineral izat ions in pre-Te rt iary rocks La Uni6n 8 Ag Volcaníc-hosted Ag lineralizations of epitherllal type Cabo de Gata Au-BEARING VOLCANIC-SED. DEPOSITS IN THE HESPERIAN MASSIF(ttt) 9 Au Gold disselinations in lIassive suIfide deposits Huelva GOLD MINERALIZATIONS IN HERCYNIAN METAMORPHIC TERRAINS 10 Au Vein-type, shear-zone hosted Fervenza 11 Au Hydrothermal, granitoid related Salave 12 Au Mixed shear-zone granitoid hosted Corcoesto 13 Au Skarn gold ores, with sulfides Carlés 14 Au 'Sb(As)-Au veins and other types Extremadura, León Au MINERALIZATIONS IN THE NEOGENE VOLCANIC PROV. OF SE SPAIN 15 Au Volc.-hosted, high-sulfidation (01' aeid-sulfate) epitherllal type R.o da1qui 1ar 16 Au Vo lc- hos ted, 10w- sul f idation (adula.ría. -se rie í te) ep ithe rlla1 type Cabo de Gata 17 Au Not volcanic-hosted mineralizations LOllo de Bas GOLD CONCENTRARIONS IN NEOGENE & RECENT DETRITAL SEDIMENTS 18 Au Gold-bearing palaeoplacers, lIainly Neogene, and placers NW Spain PRECIOUS METALS CONCENTRATIONS IN GOSSAN FORMATIONS 19 (t) Au Supergene Au-Ag ores in gossan fro. lIassive sulfides (type 9) Rio Tinto, Huel va Au, Ag 1 PGE or Platinul Group ElelentB. (tt) In base letal-Ag (bIAg) deposits oC types 6 ¡ 1, Ag has been onl, Ion as a bJ-product. (t**) In type 9 gold iB Ion as a b,-product, the sale aB silver. CAD. LAB. XEOL. LAXE 20 (1995) rences are rather excluded than classified in a wrong place. This choice, intended to avoid mistakes or inconsistencies, should by no means neglect or deny the possible value of those poorly known occurrences that might well be worth sorne research: a special group (Type 14 in the classification) includes sorne of them. So this classification can be considered as an open one, in which further groups could be established if necessary-this might happen with sorne deposits of the type just mentioned, should further research prove them to be different-, but an effort has been made in order to keep it as simple and logic as possible; the preliminary proposal by CASTRüVIE]ü (1993) has been revised to approach this principIe, resulting in the typological classification of Table 3, which is now presented 3• Since criteria used for the classification ofmineral deposits are often controversial, a typological scheme based on broad and well established geological data, has been chosen as the most useful for exploration, and, given its descriptive character, also as the best to keep controversies in a sound frame. Deposits have been first grouped after their geological enviroment, and then characterized into types, each defined by a set of general features. These features should be observational, unbiased by personal interpretations. In sorne cases, however, their use can be contested. For instance, it could be argued that thegossanAu-Agdepositsoftype 19, which are surficial bodies produced by supergene enrichment ofmassive sulfide deposits with weaker precious metals dissemination (tipe 9), need not be classified separately from these. N evertheless, several reasons speak in favour of such a distinction: even if they elasificación metales nobles 259 occur tightly related, their genesis occurs unquestionably at a quite different environment and time, their geometry has different constraints, exploration strategies and techniques differ accordingly, as also do their mining, ore-processing and metallurgy; last but not least, the gossan bodies are true precious metals deposits, which the massive sulfide orebodies are not (up to now, Au and Ag are won from them only as by-products), and the former will be exhausted in sorne years, while nobody has yet predicted the exhaustion ofthe SW Iberian Pyrite bodies. Sorne broad genetic criteria can therefore be useful for the classification. They are accepted, only if they are easily observable, clearly defined and unquestionably based on facts. However, arguable unnecessary distinctions are to be avoided: so in the Fuenteheridos silver deposit, consisting of small sulfide and gossan bodies, both these are grouped together in type 5, since their distinction would have hardly any practical value. In order to avoid repetitions, deposits or prospects with more than one precious metal are classified after the main one (the other being considered as by-product), and consequently described only in the paragraph corresponding to that metal: so gossan «silver deposits» are to be found under gold (type 19), the same as «silver-bearing» massive sulfide deposits (type 9). Finally, base metal deposits having precious metals only as by-products are out of the scope of this paper, but have nevertheless been included in the classification (Table 3), unless their contribution is insignificanto Should this not be the case, such important deposits as the massive sulphide bodies of the SW Iberian Pyrite Belt (see reserves, Table 4), would have deserved no mention. 260 Castroviejo A SUMMARY DESCRIPTION OF DEPOSIT TYPES AND THEIR EXPLORATION / MINING SIGNIFICANCE The typological classification of T able 3 and the following comments attempt to summarize present knowledge ofthe Spanish precious metals geology. The occurrences mentioned can be located and referred to their geological background in figs. 1 (general), 2 (Neogene calc-alkaline volcanic province ofSE Spain), and 3 (NW Sector of the Hesperian Massif), while sorne basic data on assumed ore reserves and grades, earliercompiledbyCASTROVIE]O(1994), can be found in Table 4 and may be useful to compare the mining importance of deposits. There are many occurrences whose individual description is not neccessary for the definition oftypes and would exceed the purpose of this paper. Instead, a typical occurrence has been chosen and will be described as representative for each type. PGE DEPOSITS P latinum Group Elements (PGE) are known to occur as concentrations in mafic / ultramafic rock bodies, which in Spain occur mainly in the NW sector ofthe Hesperian Massif (Galicia) and in the Alpine Domain of Southern Spain (Málaga). Sorne findings of PGE are known in both areas, which belong to different specific types: 1) In the Hesperian Massif: the ophiolitic, polymetamorphic type, exemplified by the Cabo Ortegal, Coruña (fig. 1 and 3), occurrences, e. g. the Herbeira Massif, showing contents of up to 6 ppm Pt + Pd (Monterrubio, 1991); similar occurrences are known in Portugal (Braganc;a and Morais CAD. LAB. XEül. LAXE 20 (995) complexes, COTELO NEIVA, 1949), or in Galicia (MONTERRUBIO et al., 1992). 2) In alpine domains: the Cr-Ni-ores of the Málaga ultramafic complexes (Ronda, Ojén, and Carratraca, fig. 1, possible subcontinental mantle slabs). This was the first type to draw attention to Spain's Pt potential -e. g. ORUETA, 1919, Serranía de Ronda-, and the only one in which Ni ores have been mined and, more recently, explored. After the pioneer works ofD. Orueta, exploration for PGE has been rather scarce (ITGE-]A, 1986-87), but several contributions have been recently published which help greatly understand the genesis and distribution of PGE. There types of ores (Cr or chromite, CrNi or chromite-Ni arsenide, and S-G or NiFe-Cu sulphide-graphite ores) have been recognized. The second of them (Cr-Ni ores) shows the most attractive PGE potential (and also Au values up to 35 ppm), corresponding to a new type of mineralization occurring in the Rifo-Betic alpine belt, apparently unique in the world (LEBLANC and ]OHAN, 1986; GERVILLA and LEBLANC, 1990). Nevertheless, traces of PGM have also been found as rare inclusions in chromite from the Cr-ores (TORRESRUÍZ et al., 1993). PGE occurrences of type 3 are found as scarce detrital concentrations in stream sediments and soils related with the above formations (ORUETA, 1919, in S. Ronda; SHASHKIN, 1992, in Cabo Ortegal: results from the E. N. Adaro exploration campaign). Sorne other PGE occurrences are known in other areas (e. g. Cantabrian Zone: PANIAGUA, 1994; Catalonian Costal Chains: MELGARE]O, 1992) whose main interest seems to be mineralogical and are therefore not characterized as prospects, n >~ ~ ~ >< tn .á.( ~ ~NCIN~. ~~~ ~ >- g N o N C0~ .. D ... 8 1--' \D \D ~ 1 . .O'·.·.·.~ • • . . A.PLASENZUELA. REAL . . . ~~' . . . - .<> .. ., . . . eso. ., GUADALCANAL I I . . IV + V • ~C.~:.:.:.:. ~UDAD . . . 9L~ . .~. . • . . . . ./l. /:A . . .. AL I . LA~ UN ION .FUENTEHERIDOS. . ~-=e~T~!E~ ~E~L~ CARTAGENA a / .. ' - . . . HUELVA I I ~r I I MESO-CENOZOIC caVER 111 ~ ALPINE DOMAINS (a.BASEMENT) 1+11 l······· -1 HERCYNIAN DOMAIN A Ag * PGM Ó Au l) I la_ ........ ~~8_0_~~_G.JATA ALMERIA o SO 160 km ~ t-¡ ~ ~. ~. ~\ ~ ~ ~ Fig. 1. Geological sketch map of the Iberian Peninsula (Castroviejo, 1994). The Hercynian Domain comprises Precambrian and Paleozoic terrains (Hesperian MassiO. The Alpine Domains are composed ofMeso-cenozoic terrains, and a Hereynian Basement. The Cover comprises pre- & syn-Alpine Meso-Cenozoie Terrains and post-Alpine Tertiary basins. (Inset: Area enlarged in fig. 2). Abbreviations for localities and prospeets / deposits eited: AL: Almuradiel (Iype 14); BC: Brués-Carballiño districts (1.11); BM: Bragan~a and Morais complexes (1.1); BR: Burón-Riaño (l. 14); C: Carlés (l. 11); CA: Carracedo (l. 13); CS: Cala (l. 13) and Sultana (l. 11) Mines; FSC: Fervenza - Santa Comba (l. 10,12); IN: Infiesto (l. 13.); L: Linares - La Carolina, Sierra Morena (1.6); LC: La Codosera (l. 10); OLM: Olivenza Monesterio Antielinorium (l. 10); PO: Pino del Oro (1.10): ROC: Ronda, Ojén, Carratraca (1.2),' SA: Salamón (1.14),' U: Usagre (1.14),' V. Villamanín (1.14). ~ ~ ~ g.. ~ N 0\ ¡......l TABLE 4 ESTIMATION OF RESERVES AND GRADES OF DEPOSIT TYPES(*) Type 5 Occurence Reserves( 1) Fuenteherídos Grade(2) 2 4 %(Pb+Zn) 3 77 Ag 47 Ag Río Tinto (Huelva) 37 Tharsis (F. Sur, Lapilla) 5 19 10/12 11 13 9 0.9 Au 2 Au Mean orebody(3) 0.03 3 Au Salave (Asturias) 16.5 2.5 Au Carlés (Asturias) 5 5/6 Au Cala (Badajoz) (. ) 10 0.07 Au Lomero Poyatas (Hllelva) 0.5 6 Au Masa Migoyas (Sotiel, Huelva) 6 2 Au Filón Norte, Tharsis 86 Masa Los Frailes (Aznalcóllar, Sevilla) 50 15 Rodalquilar, mean orebody(3) 18 Type orebody 0.8 Au 0.7 Au 0,5-1 5-25 lIill.m3 70 Ag 1-3 Au O,1/0,15g/113Au (*) Type indicated by number in Tab.1. (l)in million tons, unless otherwise stated; these numbers are estimations of existing (not yet mined) reserves (june 1993; more data: Castroviejo, 1994). (2)in ppm Au or Ag, unless otherwise stated. (3)Data given apply only to individual, discrete bodies. The reserves of a district, or even a mine, would usually be a multiple ot the tonnage given, depending on how many bodies have been defined (mean grades are estimated to be the same). E. g. in the Rodalquilar district several of these separate bodies are known, which belong to different owners (mainly Transacción and IN! or State owned mines); a reasonable assurnption of 5 orebodies -total reserve evaluation is not yet finished, so these rnay be rather conservative estimations- would allow to expect a total Au metal content of sorne 2.5-3 t. Sorne deposits belonging to types 10 to 13 in NW Spain could be expected to contain several orebodies, with a total metal content of sorne 5-15 t Au (i.e. 210 million t reserves, grading 1.5-5 pprn Au). (4)Concentrates of this iron mine grade 6-8 ppm Au. CAD. LAB. XEüL. LAXE 20 (1995) unless further work demonstrates their mining potential. SILVER DEPOSITS Silver belongs to traditional Spanish mining and occurs in a variety of deposits types and epochs. Given its typical association with base-metals or gold, silver is very frequently won as a by-product of those metals, and the corresponding deposits should therefore not be classified under the heading of silver, but under Pb-Zn or Au. Consequently, Au-Ag deposits are discussed under gold; as for Pb-Zn-(Ag) deposits, they are sensu stricto out of the scope of this work and shall not be dealt with in detail, but since much of the traditional Spanish silver production is due to these deposits, they will at least be classified (type 6) and briefly characterized. The following types have been defined: * Silver and/or base-metal-(silver) deposits, occurring in Hercynian terrains (mostly in the Hesperian Massif): -Meso- to epithermal silver veins in Hercynian metamorphic terrains (type 4). This is a very broad group, which accounts for most of the traditional Spanish silver production and which can actually embrace several classes of deposits as far as environment and genesis are concerned: e. g. Hiendelaencina (Guadalajara), Plasenzuela (Cáceres), Guadalcanal (Sevilla). The most productive and famous Spanish silver mines, Hiendelaencina and Guadalcanal, belong to this group. The deposits of Hiendelaencina (MARTINEZ FRIAS, 1992) and others of Clasificación metales nobles 263 the same Sistema Central district have been interpreted as epithermallate-Paleozoic Agbase metal concentrations 4 , related t~' extensional tectonics and to calc-alkaline Carboniferous/Permian volcanism (CONCHA et al., 1992) their genesis is yet controversial (TORNOS et al., 1993; CONCHA et al., 1993). The Plasenzuela mines won silver from meso-(epi)thermal metasediments of the Complejo EsquistoGrauváquico (Schist-Greywacks Complex) and spatially related to a granitic intrusion (LAGO etal., 1989); this deposits show sorne close similarities with those of the Coeur d' Alene district, Idaho (USA). The Guadalcanal deposit, which shows sorne close similarities with the Kongsberg (Norway) and Cobalt (Ontario) deposit types, has a complex arsenide, antimonide and Agsulphosalt mineralogy (CASTROVIEJO, 1990 b), whose precipitation seems to be controlled by the reaction of Ag-bearing hydrothermal fluids with Fahlband metabasite rocks. -Silver and base metal deposits related to volcanic-sedimentary and / or carbonate formations (type 5). This apparently large group, is in this classification restricted to volcanic-sedimentary or carbonate-hosted silver and base metal occurrences in which Ag is not a subordinate by-product with respect to gold 5 , and is typically represented by the volcanogenic Fuenteheridos (Sierra de Aracena, Huelva) deposit, recently discovered by Charte Expl. It consists ofstratiform, possibly volcanogenic, sulphide bodies (pyrite, sphalerite, galena, and Ag-sulphosalts, with barite), hosted by limestones and volcanic sedimentary sequences of Upper 264 Castroviejo CAD. LAB. XEOL. LAXE 20 (1995) o JUMILLA • N , o I 1O I 20 I 30 I 40 I MURCIA o 50 I 4.\r km L. DE BAS~ ~'. CP LA UNION MAZARRON CARTAGENA \J O c>... t_~ ,---- _~----.::::O:....-- O .~ ~ --' AGUILAS S. ALMAGRERA HERRERIAS / PALAI CARBONERAS ALMERIA C. GATA/ TRANSACCION RODALQUILAR SAN JOSE SANTA BARBARA VOLCANIC ROCKS fZZZl 1-1 101 CALC-ALKALINE C.A.-POTASSIC/ULTRAPOT. BASALTIC Fig. 2. Distribution ofNeogene Volcanic Rocks in SE Spain (area corresponding to inset infig. 1) and location of deposits prospects discussed (modified from López Ruiz and Rodríguez Badiola, 1980). The calc-alcaline potassic and shoshonitic rocks and the ultrapotasic rocks of these authors are represented together, for reasons of scale, as «c. A. potassic / ultrapotassic rocks». Mine's symbolscorrespondtoPb-Zn-Ag(Fe,Mn, Sn,Sb)orAuminingdistricts.Abbreviations used: CF Carboneras Fault; CP Cabo de Palos. Clasificación metales nobles CAD. LAB. XEüL. LAXE 20 (995) ~OPHIOLlT[T.C. 265 occurring in the Hesperian Massif (most of them) or in the Hercynian Basement of Alpine Chains (Pyrenees), usually granitoid- or metamorphic-hosted6 : type 6. ~ I.4ETAI.40RPHIC/POLY-T.C. y THRUST MORAIS Te. Fig.3. Distribution of allochthonous units in the Galicia-Tras os Montes Zone (Western Galician and N orth Portuguese sectors of the Hesperian Massif, modified from: Ribeiro et al., 1990, and Quesada, 1992), showing the position ofthrust complexes (TC), and of sorne major shear zones related to Au concentrations, corresponding to the margins of the Malpica-Tuy Unit, MTU, and to the Pontedeume Lineament, PI. Gold distries andprospeets: AR Aranga; ARM Armada; COR Corcoesto; D Donas; PER Pereiro; RE Remourán; RO Roñón; T Tomiño; TR Traviesas; Wf West Santa CombaFervenza area (mines & occurrences of Meanos, Fousas de Vila, San Martiño, Limideiro, Vilarcovo, Albores, and Rial, along the sheared Eastern margin of the Malpica-Tui allochtonous U nit, described in Castroviejo, 1990a, and in fig. 4, below). The Cabo Ortegal, Ordenes, Braganc;a and Morais TC comprise ophiolite complexes hosting PG E, type 1, metal/oteets, ineluding the Herbeira Massif(HM). Proterozoic to Lower Cambrian age, and enriched in silver by secondary supergene processes, which led to the formation of a gossan body aimed at as main mining target (ESPI, 1990). This peculiar silver upgrading needs not be neccessarily a feature ofthe type. -Veint-type Pb-Zn-(Ag) deposits, This group, in which silver appears only as a by-product, has been very important (e. g. the Sierra Morena districts) for Spanish and European mining, but in spite of various exploration efforts (e. g. RÍOS, 1980, in Linares, Jaén; CASTROVIEJO & MORENO, 1983, in Cierco, Lérida) all the mines still working deposits of this type in the last years, as those of the Linares - La Carolina area (J aén) or Cierco (Pont de Suert, Lérida), have been closed down, due to the fall in metals' prices and to the near exhaustion of reserves, after decades of continuous mining. * Silver and/or base-metal-(silver) deposits (volcanic-related and of Tertiary age) occurring in the Neogene Volcanic Province of Southeast Spain, in a variety of environments: -Fe-Base metal-(Sn, Ag) vein-type, replacement and disseminated deposits related to shallow Tertiary intrusives in various Hercynian and Mesozoic lithologies from the Betic Chains (type 7). They had since pre-Roman times an unquestionable mining significance... until recently: e. g. La Unión, Cartagena (Fig. 2). The deposits of this district, which used to be described, when active, as the world's lowest grade Pb+Zn mines, have a controversial genesis (PAVILLON, 1969; OEN et al.} 1975;OVEJEROetal.} 1976),towhich several factors may have contributed (preTertiary concentrations, epigenetic subvolcanic hydrothermal circulation, etc.); nevertheless, as a type, they can be con- 266 Castroviejo CAD. LAB. XEOL. LAXE 20 (995) veniently characterized as concentrations spatially related to shallow intrusives of the Neogene Volcanic Region ofSE Spain, even ifthey are hosted by metamorphic Hercynian or by Mesozoic formations. Spanish gold production, both as: by-product gold, disseminated in massive sulfide orebodies (type 9), very well represented in the SW Iberian Pyrite Belt, Huelva and Sevilla Provinces, fig. 1), and as -Epithermal Pb(Zn)-Ag(Au) and Ag ores related to N eogene calc-alcaline volcanites (type 8), which can be volcanichosted, sediment-hosted (not yet proved) or even hosted by Hercynian lithologies (transitional to type 7). * Supergene gold concentrations in gossan orebodies derived from the aboye (type 19, e. g. There are not many examples which can be properly considered as silver deposits, i. e. in which silver may be the main precious metal; two of them should perhaps be cited as the most typical: the occurrence of Herrerías, Almería, for silver (MARTINEZ FRIAS, et al., 1989 & 1992); and the likely economic Zn-Pb-Ag body of Mazarrón, Murcia -under exploration by Navan-, for base metals & silver (MORALES and FENOLL, 1990). Other examples, in the Cabo de Gata (e. g. Santa Bárbara mine) and Rodalquilar(e. g. Niñas and Consulta mines) districts, Almería, will be treated under gold, which is now looked as the most important metal ofthese districts (see types 15 to 17). GOLD DEPOSITS Gold has a long tradition of mining in Spain and, the same as silver, occurs in a variety of epochs and deposit types, which can be classified as: - Volcanic-sedimentary deposits in Hercynian metamorphic terrains: They are the first source of present-day Río Tinto and Tharsis / Filón Sur and Lapilla mines, Huelva); their exploration has been very successful, leading to a considerable increase ingold production (GARCIA PALOMERO et al., 1986); they have been divided in several (sub)types and characterized by these authors. * Hypogene gold concentrations in Hercynian metamorphic terrains: These ores, already won in pre-Roman times, were among the most searched in the last years, especially in the Hesperian Massif (NW Iberia, Extremadura). The wealth of information thus produced, although not always published, allows the systematic classification ofthese prospects and deposits in types 10 to 14 (Table 1), sorne of which (types 10,11 and 12)mayappearfrequently interrelated or mixed. Even if the distinction of these might seem artificial, since shear zone related deposits are also very frequently granitoid or porphyry related and viceversa, it is useful to distinguish a type ofGranitoid related deposits (type 11), not necessarily implying the existence of ductile deformation or shear zone development, while the mixed type 12 implies a relationship with both granitoids and ductile deformation. Clasificación metales nobles CAD. LAB. XEOL. LAXE 20 (1995) The description ofsorne examples (fig. 1 and 3) may help define the geology of the different types: those of the West Santa Comba-Fervenza area, Coruña (CASTROVIEJO, 1990a) for type 10 (Veintype, shear-zone hosted); Corcoesto, Coruña (GOUANVIC, 1983) for type 12 (mixed granitoid & shear-zone type); Salave, Asturias (HARRIS, 1980 a, b) for type 11 (Hydrothermal, granitoid related); and Carlés, Asturias (GARCIA IGLESIAS and LOREDO, 1990; MARTIN-IZARD et al., 1993) for type 13 (Skarn gold ores). The West Santa Comba-Fervenza shearzone occurrences (fig. 3), show these typical features; shear zones appear as major controls; there is evidence of fluid overpressure in a ductile to brittle transitional regime, with cyclic or repetitive rupture of the structures, as demonstrated by textural microanalysis (fig. 4); the rupture is followed each time by hydrothermal circulation and alteration, vein infill and breccia cementation; granites or porphyries are frequently observed. They are similar to other Hercyninan shear zone gold deposits in Europe (e. g. in the French Massif Central, BONNEMAISON andMARCOUX, 1987) and, as compared to the typical vein-type, shear-zone hosted, pre-Cambrian gold deposits found in greenstone belts (as in the Abitibi Belt, Canada), they are smaller in size and tonnage and tend to occur in higher grade (up to catazonal and anatectic) metamorphic rocks, in sequences where mafic volcanics are not so abundante Favourable areas for these deposits are known along the tectonic contacts of various allochtonous units in the Hesperian Massif (see prospects in fig. 1), as in Galicia (fig. 3; Xunta de 267 Galicia, 1991; ITGE, 1993 or in the Central Iberian Zone, and also in the Hercynian basement of the Pyrenees (Vall de Ribes district: ROBERT, 1980; AYORA et al., 1992). - Granitoid related (type 11) This deposits show abundant hydrothermal alteration related to ore (sulphides and native gold) deposition, and gold may be associated with sorne specific facies. The «Salave-type» of gold deposit is defined by HARRIS (1980b) as «one formed in almost any king offeldspar-quartz-ferromagnesianbearing rock, probably in an area of major tectonism with a zoned alteration facies of decreasing carbonatization, albitization, desilicification, sericitization, and texture destruction away from a disseminated gold mineralization associated with pyrite, arsenopyrite, stibnite and minor amounts of other sulphides». This «Salave-type» is here considered as a particular case of granitoid related gold deposit, a larger group also including other bodies in which sorne ofthe features mentioned are lacking or are different, as happens in the Brués, Carballiño and Tomiño granite-hosted vein deposits in which gold deposition is associated to argillic, sericitic or greisen-type alteration. - Mixed shear-zone / granitoid hosted (type 12) This type is represented by the Corcoesto (Coruña) body and various prospects in the Fervenza, W ofSanta Comba (Coruña) area, Pino del Oro, Zamora, etc. Hydrothermal (sericitic, argillic...) alteration is usually intensive (less so in Corcoesto) and gold ores associated to arsenopyrite, sulphides or 268 Castroviejo CAD. LAB. XEüL. LAXE 20 (995) lb 18 Il·a III a IC IIC 111 b Ir1 e Flg. 4. A typological characterization of sulphide ore textures from shear zone Au deposits, based on observations in the West Santa Comba-Fervenzas area (modified from Castroviejo, 1990a), showing evidence of repeated brecciation, hydrothermal infi11 and sulphide precipitation. Black: arsenopyrite; white: silicate gangue; S: trend of main S-surface. Type 1: disseminated ores (a: idiomorphic; b: lenticular; c: microclasts): Type 11: stringer or fine-banded ores (a: microfissures and S-planes; b: microshears; c: microclasts); Type 111: massive ores (a: vein fi11; b: breccia cement; c: cataclastic) as a general rule, deformation and age increase from ato c. CAD. LAB. XEOL. LAXE 20 (995) sulphosalts, tend to occur in quartz veinlets. Chloritization and potassic alteration may be precursor hydrothermal processes, possibly related, as retrograde phenomena, to the deformational history of the structures. Recent research on deposits of this type (BOIRON etal. andCATHELINEAU etal., 1993) resulted in a model relating gold concentration to the final events of a complex sequence, ending with the circulation of low-temperature, low-salinity aqueous fluids at nearly hydrostatic pressures, in conditions similar to those of a geothermal system. These late fluids, assumed to be responsible for the gold mineralization, may have a likely meteoric origin, and need not be related to the magmatism. Instead, the strong rheologic contrasts involved, e. g. between granite and schists, contribute to enhance the brittle behaviour, i. e. the permeability, of certain lithologies (granite lenses or quartz veints), thus exerting a major control on fluid circulation and on gold precipitation, what might explain the spatial relationship ofthe ores with granites or with (preexisting) quartz veins. - The Carlés skarn body is related to a granodiorite intrusion in Devonian limestones; gold and electrum occur in copperrich skarn lenses and subordinatequartzarsenopyrite-chalcopyrite veinlets, with occasionalleollingite, pyrrhotite, etc.; the refractory character of the ore seems to be the hardest problem for its exploitation. Other examples are know in the same (Salas, controversial genesis) or other areas (fig. 1) in NW Spain, as Carracedo, Palencia, and Infiesto, Asturias, or in the Pyrenees (Maladeta, s.) LOCUTURA and BELLAN, 1987; near Andorra s. SOLER et al., 1990). Nevertheless, theonly gold productionfrom Spanish skarn deposits at apresent comes as Clasificación metales nobles 269 by-product from the Cala iron ore mine, Badajozprovince(see 2), whichisonlyafew km away from the now exhausted granitoidrelated Sultana gold mine, in SW Spain. - Sorne other prospects or deposits, generally of scarce mining importance for gold as far as known, have been grouped in type 14, most typically represented by SbAu or As-Sb-Au veins in Hercynian terrains, described by different authors in the Hesperian Massif. The many showings included in this group -e. g. Herrera del Duque: GUMIEL and ARRIBAS, 1987; Almuradiel: LEAL and CASTRVIEJO, 1990; Usagre: (TORNOS and LOCUTURA, 1988; BURÓN and VILLAMANÍN: PANIAGUA et al., 1988 a & b- are not necessarily resulting from the same genesis or characterized by an identical geological environnment. Having not attracted much companies attention as gold prospects, they are often poorly known yet; a more precise geological characterization resulting from further research might lead to a subdivision of the group, broadly described as mesoto epithermal vein-type or epigenetic SbAu or As-Sb-Au concentrations, in different types 7 . * Gold, gold-silver orgold-silver & base metals mineralizations occurring in the Neogene Volcanic Province o[ Southeast Spain: They correspond to various epithermal types of Tertiary age and are related to the calc-alkaline volcanic rocks outcropping mainly in the Almería province (Figs. 2). They are by now essentially represented by volcanic hosted deposits (types 15 and 16: high-sulphidation or acid-sulfate, and lowsulphidation or adularia-sericite types, as CAD. LAB. XEüL. LAXE 20 (995) 270 Castroviejo CINTO JeNIM.'TES (IU) PRE-CALDERA ..........~---- .....IIIIIiI"~ ~)IC ~ ... DOMP ,/ OACITIC MAGMA 1- PRE--COLLAPSE VOLCANISM t--- 2-FIRST IGNIWfRITE N{) COll.APSE-1 CINTO SECTOR - - -... w w 3- REStR3ENCE (CINTO CALDERA) 4-SECOOD tGNMTB. ERUPl1CH ANO COLLAPSE-II w 5-RESURGENCE AND LATE ERUPT. ACTIVITY EPlTHERMAL MINERALlZATION (Au) 6-MESSINlAN TRANSGRESSICW 7-POST-MESSINIAN UPUFT ~ EROSION Fig. 5. Serial ENE-WSW simplified sketch sections of the Rodalquilar volcanic field, showing the successive stages in the genesis and evolution of the caldera structures related to the gold mineralization (modified from Castroviejo, 1988). The domes being intruded and the volcanic materials being erupted in each stage are represented in black. CAD. LAB. XEüL. LAXE 20 (1995) defined by HEDENQUIST, 1987 or by HEALD et al.} 1987); non-volcanic hosted bodies (type 17) have been worked for Pb (Zn) and Ag, while for gold they have only been recognized as prospects (e. g. at the Sierra de Lomo de Bas, Aguilas-Mazarrón, Murcia), but the potential of the region for this type, including sediment-hosted, Carlin-type deposits, should not be neglected. - The-high-sulfidation (type 15) Is well characterized by the Transacción and other deposits ofthe Rodalquilar district, Almería (fig. 2)} deposits (ARRIBAS et al.) 1988); CUNNINGHAM et al.} 1989, RYTUBA et al.} 1990), related to the Cinto and Lomillas calderas (fig. 5) and to their 11 to 10 m. y. old post-collapse magmatic and hydrothermal activity, producing intensive alteration and gold deposition in veins and disseminations in the hostrock. Native and telluride gold ores are associated to hypogene silicic and advanced argillic alterations. Alteration associations are arranged in successive zones, away from the gold orebodies: silicification, with formation ofvuggy-silica, alunite-pyrophyllite or advanced argillic zone, sericitic / argillic and outer potassic / propyllitic zones. The Transacción deposit was developped into an (ephemeral) mine in the last decade. The Palaí prospect may be another example. - The low-sulphidation (type 16) Is represented by the Cabo de Gata} Almería (fig. 2)} deposits (Santa Bárbara mine, etc.), which can be broadly described (CASTROVIEJO, 1990c) as: vein type base metal-silver orebodies, with subordinate8 Clasificación metales nobles 271 gold and with quartz or chalcedony ( + barite, adularia, carbonate, sericite and clay) gangue, showing typical vein-fill and banded textures, hosted by the strongly altered rocks of an about 12-11 my. old andesitic dome field, in which no Tertiary or older sediments outcrop (fig. 6). The associated alteration sequence (away from the veins) consists of: silicification, quartz-sericite (phyllic) alteration and argillic alteration, transitional to the adularia and propyllitic assemblages typical ofthe country rock. A local hypogene advance argillic alteration can occasionally be observed. Frequent breccia bodies witness ofrepeated explosive activity related to hydrothermal discharge, and the level of formation seems clearly deeper than in the mostly very shallow orebodies ofRodalquilar (Cerro Cinto). - Not-volcanic hosted epithermal bodies (type 17) Are at present more scarce. Nevertheless, the Lomo de Bas occurrence (CASTROVIEJO et al.) 1990 a & b) is an interesting exploration example, suggesting a larger mining potential of the SE Spanish Neogene volcanic province, from Cabo de Gata, through Sierra Almagrera, Mazarrón, etc. to Cartagena/La Unión. It is related to hitherto unknown Tertiary porphyritic outcrops (found through remote sensing techniques, following a metallogenetic model), intruding the metamorphic Paleozoic terrains ofthe Betic chains, northwards of Aguilas (fig. 2). * Sedimentary gold concentrations in Neogene and recent detrital formations: gold-bearing paleoplacers and placers (type 20) a) , N ~ t b) BF ..... ~ -.J ~ C) ,.,. ~ ... ./ sw ZPHA (7)\ .... S8 ~ HE ~ ~ ~. ~ ~. ., • • •_-.f -- - - - - -- (7) CG o 1 I i 2 km I o PUOCENE/OUATEIUWf1 SEOI.. ENTS ~ CORE-lOME or HYOROTHERWAL ALTERAnON [2] RHYOUTIC/OACITIC OYI([S D E2J ... UPPER (AHOESmC) VOLCAHIC SERIES LOWER (RHYOUTIC) VOlCANIC SERIES ~ VEIN , ...... ' FAULT /'" CONfACr ~ OLO "IHE .... ...... ROAO Fig.6. Preliminary geological sketch map (a) and scheme showing field relations (b, idealized NE-SW section) in the Cabo de Gata volcanic and vein field, Almería (modified from Castroviejo, 1990 c, and Fernández Soler, 1992). The volcanic rocks of the Lower Series are mainly rhyolitic and dacitic ash flows domes and breccias, while in the Upper Series andesitic domes, flows and breccias are dominant. The corezone of hydrothermal alteration shows intensive argillic/phyllic, occasionally advanced argillic, alterations, superimposed on an earlier pervasive potassic alteration. Compare with fig. 5: no caldera collapse structures are observed in this case. Abbreviations: ADF Andesitic Dome Field; AF Ash-flow tuffs; BB Breccia and autoclastic breccia bodies; D Domes; F Lava flows; LPA Late (unaltered) pyroxene andesites; ZPHA Zone of Pervasive Hydrothermal Alteration. Localities/mines: CG Cabo de Gata; PF Pozo de los Frailes; BF Boca de los Frailes; SB Santa Bárbara Mine. n > ~ &: ~ ~ tT1 O ~ &: ~ tT1 l'V o ~ \O \O ~ CAD. LAB. XEüL. LAXE 20 (1995) Occur mainly in NW Spain and have been extensively mined by the Romans, contributing very much to Spanish prehistoric and ancient historic production, but in spite ofthe impressive works that can still be observed (e. g. Las Médulas and Las Omañas, León) and of archaeological and exploration works undertaken by several institutions and companies no modern mining has been developped. A detailed characterization of the deposits of this large group exceeds the purpose of this paper and can be found in the works ofDOMERGUE (1970), DOMERGUE & HERAIL (1978), SANCHEZ PALENCIA-RAMOS (1983), HERAIL (1984), PORTER et al. (1989), PEREZ GARCIA & SANCHEZ PALENCIA-RAMOS (1992),a. o. Thistype occurs in other areas as well: e. g. the goldbearing plio-quaternary alluvial fans of Caniles de Baza (Granada) and Ugíjar (Almería), related to the erosion of the Nevado-Filábride and subordinately, Alpujárride Complexes in the Alpine Domains of the Betic Chains 9 . SOME PROBLEMS FOR FURTHER RESEARCH The foregoing discussion should have shown the noteworthy progress made in the last decade in many aspects ofthe geology of Spanish precious metals deposits, but there are still many unsolved problems whose solution would be important for further development. Among these, those dealing with exploration -as the ore processing research of the refractory gold ores so frequent in NW Spain, the detailed definition of ore controls and reserves of the usually irregular shear-zone deposits, the appraisal of the precious metals potential of the SE Clasificación metales nobles 273 Spanish Volcanic Province, etc.- have already been stressed by CASTROVIEJO (1994) and will not be discussed any further. The research and precise definition of the many showings or prospects grouped in type 14 is also to be done, and might lead, as already stated, to sorne revision ofthis group. New models, if proved to be significant, could lead to new sub-types or even types. Among them, the epithermal and Carlin types ofAu deposits (se below) proposed by several authors, or the gold-bearing hydromagmatic breccias defined by JAHODA (1987) in NW Spain, occurring in the early Paleozoic Vegadeo limestones and Los Cabos Series metasediments, related to major strike-slip faults and to gabbroic intrusions. Another question dealing essentially with typology is the more precise definition of the concept of epithermal deposit and its characterization, a question dealing with the assumed existence of Paleozoic epithermal (s. s.) deposits in Spain. This term can be -and has been- correctly applied to deposits of the calc-alkaline Volcanic Province of SE Spain. It has also been used -and sometimes contested- for several deposits in the Hesperian Massif (e. g., Hiendelaencina, various occurrences in NW Spain, etc., types 4 and 14 in Table 3). Much argument could perhaps be spared if every author made'an effort to define exactly what he understands under that concept while applying it to a deposito In fact the term seems to have become very equivocal in the literature. For sorne it may mean a model or a type (in fact several types, e. g. low- or high-sulphidation) of volcanic deposits in the present american use, but for others rather a set of physicochemical conditions including even plutonic deposits, in 274 Castroviejo a classical european use (NIGGLI, in SCHNEIDERHOHN, 1962). The precise geochemical research of the fluids involved and their comparison with typical epithermal fluids should help solve the problem. Sorne rigorous characterizations already existing in the literature, as those by HEDENQUIST (1987), by HEALD et al., (1987), and by WHITE and HEDENQUIST (1990) among others, should be used as reference. CONCLUSIONS Spain, first precious metals mining country of the EU (European Union), has been exploration target for many companies, and consequently the knowledge of the Spanish precious metals geology has been increased, in the last decade, under the influence of favourable market conditions especially for golde This has produced sorne new mining developments and a wealth of information, which the author has tried to summarize through the typological classification ofTable 3. A comparison with former typologies (tables 1 and 2) allows to appraise the recent developments due to various contributions. Precious metals concentrations occur in Spain in Hercynian and Alpine domains, and in the Meso-Cenozoic Cover. They have been classified following a descriptive typology, relying on geological facts rather than on interpretations, after the scheme in Table 3, which stablishes 19 types, thus simplifying a preliminary scheme by the author (1993) with 20 types. * The main types of mineralizations in Hercynian terrains are: the ophiolitic (type 1) PGE occurrences in the NW Hesperian Massif (Cabo Ortegal, Herbeira); vein-type (Guadalcanal, Hiendelaencina, type 4) and CAD. LAB. XEOL. LAXE 20 (1995) strata-bound (Fuenteheridos / s.a Aracena, type 5) silver deposits in the Hesperian Massif; hypogene gold mineralizations (types 10-13), skarn and vein types (shearzone or granite-related) or other (tipe 14); gold disseminations in volcanic sedimentary massive sulphides (SW Iberian Pyrite Belt, type 9). The supergene gossan gold & silver deposits (type 19) derived from the latter are actively mined at presento * In Alpine domains, the main types are: the PGE occurrences (t. 2) in gold bearing Ni-arsenide ores of ultramafic formations, Serranía de Ronda (Málaga), and the various types ofgold / silver / base metal deposits in the Neogene volcanic province ofSE Spain, mostly epithermal and with an attractive potential for exploration (types 7-8 and 15 to 17). Finally, in the Meso-Cenozoic Cover, well known (type 18) detrital gold concentrations (e. g. León province) occur. Sorne problems demanding further research have been underlined, which are relevant for the correct understanding and classification ofthe Spanish precious metals deposits, as the more precise definition of many type 14 occurrences and of sorne controversial epithermal (?) deposits (see the preceding section, for further questions). As far as exploration is concerned, no mining development has been achieved for PGE's. Results for silver have been more rewarding in those types in which the precious metal is associated, as by-product, with gold (see type 19) or with base metals (as the promising Zn-Pb-Ag prospect of Mazarrón, Murcia), less so, for main metal Ag (e. g., the small silver and base metal body of Fuenteheridos, in s.a Aracena, Huelva, type 5). For gold, the volcanic sedimentary ores of the SW Iberian Pyrite Belt are still by far the country's main CAD. LAB. XEüL. LAXE 20 (1995) source, both as a by-product in the sulfide mines (type 9) and, principally, as the main metal in the gossan bodies (type 19) related to the former. The mining results of exploration on these gossan bodies have been really rewarding (Rio Tinto and Tharsis, Filón Sur & La Lapilla), but are restricted to a very limited area. In the Hesperian Massif ofNW Spain, the refractory character ofthe ores or the small size and irregularity of the orebodies have been a serious handicap, preventing mining development for otherwise attractive type 10-13 prospects (as Carlés, Salave, etc.). The (mostly Neogene) sedimentary paleo-placer and placer gold deposits in NW Spain show also an interesting potential, but have not reached the production stage. The Tertiary epithermal gold ores from the Neogene cal-alkaline Volcanic Province of SE Spain have become a significant potential source of gold, although the last mining operation (the lowgrade, open-pit Transacción Mine, elasificación metales nobles 275 Rodalquilar, Almería type 15) has been recently closed. Research done allows the distinction of types 15 to 17, i. e. volcanichosted (high-and low-sulphidation) and not volcanic-hosted types, and the extension of target areas in the region. ACKNOWLEDGEMENTS The author wishes to thank an anonimous reviewer for his constructive criticism and his colleagues J. A. Espí, C. Quesada and J. Locutura (ITGE), for their help and critical comments, as well as F. Latorre, J. Faura, and E. N. Adaro/DGM, for their support and permission to publish the parts of this work dealing with research done for E. N. Adaro/DGM. He also wíshes to acknowledge Mr. Ph. Lagny and Chronique de la Recherche Miniere who allowed hím the publicatíon of sorne figures and Table 4 from a paper by the author. N O T E S 1 The fol1owing remark by this author, as recently as 1984 (op. cit.), is noteworthy: «'El encaje de los yacimientos auríferos españoles en el marco de cualquier clasificación tipológica de las existentes a nivel mundial ofrece dificultades prácticamente insoslayables en el momento actual, si se pretende efectuar con un mínimo de rigor metalogenético. Esta imposibilidad se basa en el escaso conocimiento que seposee sobre la mayor parte de las mineralizaciones dado que, en general, las explotaciones minerasy los estudios correspondientes se remontan a épocas bastante lejanas». 2 Besides, sorne ofthe criteria employed would need sorne further explanation / discussion to avoid sorne apparent inconsistencies: e. g., why are types 1,2 & 3 not inc1uded in the Hercynian type, n.O 4? 3 After this work was sent to the editor (apriI1994), another c1assification ofAu deposits was presented by R. Urbano (1994), based on the already discussed criteria of Burckhalter, and commenting sorne recent work by ITGE. 4 Accordingly, and in spite ofevident differences in environment and age, these deposits have been compared with those of Herrerías-Sierra Almagrera (s. below), which are related to N eogene volcanism and c1assified under Type 8, as defined here ('Table 3). The controversial character ofthe underlying genetic interpretation cannot but support the scheme proposed in Table 3, relying rather on facts than on interpretations. s The typical massive sulphide orebodies ofthe SW Iberian Pyrite Belt, in which silver is only a by-product, are discussed under gold, which is currently their main precious metal. 6 Recent genetic interpretations of sorne of these deposits (e. g. Johnson et al., 1993 for Cierco) may be controversial, but are stil1 compatible with this typology, based on general features and on the geological environment. 7 An example ofthis might be the study -published after the presente typology was defined- of the Villamarín (León) ores by A. Paniagua (1994), after wich they represent a Cu-Co-Ni-Au-U & PGE-bearing epithermal type, explained by a model typical for the 276 Castroviejo Cantabrian Zone -also shared by other prospects-, implying a polyphase enrichment of the various metals at different stages. CAD. LAB. XEOL. 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